Synchronous belt drive systems are used extensively in industry as substitutes for chain drives or gear trains to transmit torque and/or translate motion between shafts.
Belt drives have a pitch line that is displaced from both the belt and the sprocket teeth and is located within the belt tensile member. The displaced pitch line introduces the problem of assuring good entry of a belt tooth into a sprocket groove with a minimum of interference at various belt loads and sprocket diameters.
The belt tooth/sprocket tooth interference problem is further compounded by belt manufacturing and sprocket manufacturing tolerances that result in small pitch differences between the belt teeth and sprocket teeth, tooling tolerances that result in small differences between the sprocket tooth and belt tooth flank profiles, polymer shrinkage during the molding process which results in a less than ideal belt tooth form, rotation and deflection of the belt teeth under load resulting in entry and exit belt tooth/sprocket tooth interference, and a chordal effect caused by differences in the sprocket groove depth/belt tooth height resulting in an apparent pitch difference between the belt teeth and sprocket teeth.
This pitch mismatch between the belt teeth and the sprocket teeth results in the upper portion of the pulley tooth, particularly the zone where the sprocket tip radii intersect with the curvilinear sprocket flanks, scrubbing the upper portion of the belt tooth flanks eventually weakening the belt tooth covering resulting in belt tooth failure.
Representative of the art is U.S. Pat. No. 4,605,389 which discloses a toothed power transmission belt with belt teeth having flank surfaces in the form of a tractrix curve and a belt sprocket with sprocket teeth having flank surfaces in the form of a tractrix curve, together, the belt and sprocket exhibiting smooth running and antiratcheting characteristics.
What is needed is a sprocket having a groove tip radii being joined to a groove arcuate conjugate flank portion by a linear flank portion. The present invention meets this need.